1. Field of the Invention
The present invention relates to a device and a method for manufacturing semiconductor single crystals by utilizing the Czochralski method(hereinafter referred to as the CZ method). According to this invention, the as-grown defect density of the single crystals manufactured can be reduced and the gate oxide film integrity can thus be enhanced.
2. Description of the Related Art
The substrates of semiconductor components are mainly made of high-purity silicon single crystal that is conventionally produced by the CZ method. In the CZ method, polycrystalline silicon lumps are filled into a crucible of a semiconductor single-crystal manufacturing device. Then thecrucible is heated by cylindrical heaters disposed therearound to melt the polycrystalline silicon lumps, thereafter a seed crystal installed on a seed chuck is dipped into the melted liquid. After that, the seed chuck and the quartz crucible are respectively driven to rotate in opposite or identical directions, and at the same time the seed chuck is lifted to grow a single-crystal silicon ingot of predetermined diameter and length.
The quality characteristics of the single-crystal silicon produced by the CZ method, such as the gate oxide film integrity, the precipitation oxygen amount, and the bulk micro defect, are depending on the heat history of the single-crystal silicon produced. Therefore, till now many improvements to the above-mentioned heat history has been made. For example, according to a method for manufacturing single crystals disclosed in Japanese Patent Unexamined Publication No. HEI 6-211591, an annular heater heated by electric power from a heating control device is supported by a support member which also serves as an electrode. The gate oxide film integrity can be enhanced by slowly cooling down the outer peripheral surface of the single-crystal silicon being lifted, and further the precipitation oxygen amount also can be made even. Furthermore, the heat history of the single-crystal silicon can be positively adjusted by changing the heating value of the above annular heater at a discretionary manner.
Furthermore, according to a method for lifting single crystals disclosed in Japanese Patent Unexamined Publication No. HEI 6-279188, a predetermined zone of a silicon single crystal being lifted is heat-treated by a multi-stage heater. According to a device for growing single crystals disclosed in Japanese Patent Unexamined Publication No. HEI 6-144987, reheat heaters are disposed in a gas rectifier which is used for guiding atmosphere gas into the chamber. In addition, according to a device for lifting single crystals disclosed in Japanese Patent Unexamined Publication No. HEI 8-119786, the heat history of single crystals produced is controlled by disposing an after-heater and coolers located above and below the after-heater around single crystals being lifted. According to a device for lifting single crystals disclosed in Japanese Patent Unexamined Publication No. HEI 6-287098 entitled, slits are formed in radiation shield cylinder installed in the furnace. Radiation heat coming from the furnace is guided through the slits to radiate on a specified portion, which should be cooled down slowly, of the single crystal being lifted.
The inventors of this invention have suggested a device and a method for lifting single crystals disclosed in Japanese Patent Unexamined Publication No. HEI 6-183876, in which an upper heater is installed above the melted liquid. The above suggestion is different from the above-mentioned lifting methods and devices proposed to control the heat history of single crystals.
However, in conventional arts, the ascending and descending mechanism is installed on the after-heater. For the purpose of keeping the interior of a single-crystal lifting device at a vacuum state, connection structures of electric power supply become complicated.
When the after-heater is fixed, the installation location of the after-heater or the heat radiation location within the single-crystal lifting device is accordingly determined. However, this will cause the following problems.
(1) The heating conditions within the furnace will change with the lifting conditions such as melt level, the introducing conditions of atmosphere gas. However, and the above arrangement can not respond rapidly to changes in the above-mentioned heating conditions. PA1 (2) FIG. 6 is a graph showing temperature variations at different lengths of a single crystal being lifted. The graph is drafted for the purpose of showing temperature variations at different portions of a single crystal being lifted by a semiconductor single-crystal manufacturing device which is provided with a heat-shielding cylinder near the melt surface so as to shield a single crystal being lifted from radiation heat. As shown in FIG. 6, the gradients of temperature graphs along longitudinal axis of the single crystal being lifted become gentle following the increase of the length of the single crystal. The conventional arts can not provide any solution to respond to gradient changes.